U.S. patent number 4,792,661 [Application Number 06/840,002] was granted by the patent office on 1988-12-20 for electric heating apparatus for regulating the temperature of a plurality of liquids.
This patent grant is currently assigned to Durr Dental GmbH & Co KG. Invention is credited to Mathias Muller, Gerhard Schmidtchen.
United States Patent |
4,792,661 |
Schmidtchen , et
al. |
December 20, 1988 |
Electric heating apparatus for regulating the temperature of a
plurality of liquids
Abstract
Apparatus for adjusting the temperature of a plurality of
liquids which includes temperature adjusting means having a
corresponding plurality of separate flow paths, a pump arrangement
for circulating the liquids through said separate paths and means
for maintaining predetermined temperature differences between the
liquids, wherein the temperature adjusting means includes a single
temperature controlling member and a number of pipes which
correspond in number to the number of separate flow paths for the
liquids of which the temperatures are to be adjusted. The
temperature controlling member and the pipes are interconnected in
heat conducting so that the total thermal impedance between the
first of said pipes and the temperature controlling member
integrated from the inlet end to the outlet end of said first pipe
differs from the corresponding total thermal impedance of at least
a second of said pipes. The first of said pipes is located directly
in heat conducting manner on the temperature controlling member and
said at least second of said pipes is carried by said first of said
pipes in a heat conducting manner. The thermal impedance defined
between said at least second of the pipes and the temperature
controlling member being thus formed by said first of the
pipes.
Inventors: |
Schmidtchen; Gerhard
(Sachsenheim, DE), Muller; Mathias (Oberstenfeld,
DE) |
Assignee: |
Durr Dental GmbH & Co KG
(Bietigheim-Bissingen, DE)
|
Family
ID: |
6265487 |
Appl.
No.: |
06/840,002 |
Filed: |
March 17, 1986 |
Foreign Application Priority Data
|
|
|
|
|
Mar 16, 1985 [DE] |
|
|
3509609 |
|
Current U.S.
Class: |
392/495; 138/33;
165/140; 165/290; 219/540; 392/480; 99/288 |
Current CPC
Class: |
F24H
1/142 (20130101); F24H 9/2014 (20130101); F28F
13/14 (20130101); G03D 13/006 (20130101) |
Current International
Class: |
F24H
1/12 (20060101); F24H 1/14 (20060101); F28F
13/00 (20060101); F28F 13/14 (20060101); F24H
9/20 (20060101); G03D 13/00 (20060101); H05B
001/02 (); F24H 001/14 () |
Field of
Search: |
;219/283,296-299,301-305,530,540 ;165/30,40,140,141
;99/281,306,307,288 ;138/33 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1199070 |
|
Aug 1965 |
|
DE |
|
2340489 |
|
Feb 1975 |
|
DE |
|
2701692 |
|
Jul 1978 |
|
DE |
|
3509609 |
|
Sep 1986 |
|
DE |
|
2173581 |
|
Oct 1986 |
|
GB |
|
Primary Examiner: Bartis; Anthony
Attorney, Agent or Firm: Philpitt; Fred
Claims
We claim:
1. Apparatus for adjusting the temperature of a plurality of
liquids, comprising temperature adjusting means having a
corresponding plurality of separate flow paths, a pump arrangement
for circulating the liquids through said separate flow paths of
said temperature adjusting means and comprising means for
maintaining predetermined temperature differences between the
liquids, characterized in that the temperature adjusting means
includes a single temperature controlling member (12) and a number
of pipes (14, 16) which correspond in number to the number of
separate flow paths for the liquids of which the temperatures are
to be adjusted, the temperature controlling member (12) and the
pipes (14, 16) being interconnected in heat conducting manner such
that the total thermal impedance between the first (14) of said
pipes and the temperature controlling member (12) integrated from
the inlet end to the outlet end of said first pipe differs from the
corresponding total thermal impedance of at least a second (16) of
said pipes, in that said first (14) of the pipes is located
directly in heat conducting manner on the temperature controlling
member (12) and said at least a second of said pipes is carried by
said first (14) of said pipes in a heat conducting manner, the
thermal impedance defined between said at least a second (16) of
the pipes and the temperature controlling member (12) being thus
formed by said first (14) of the pipes.
2. Apparatus according to claim 1 characterized in that the pipes
(14, 16) each have different wall thicknesses.
3. Apparatus according to claim 1 characterized in that the pipes
(14, 16) are each coupled thermally to the temperature-controlling
member (12) over sections of different length.
4. Apparatus according to claim 1 characterized in that said pump
arrangement includes a circulating pump with controllable delivery
associated with the first one of the pipes (14), which pipe has the
lowest thermal impedance with respect to the temperature-adjusting
member (12).
5. Apparatus according to claim 1 characterized in that temperature
sensors (34, 38) are fitted to the end sections of each pipe (14,
16) on its outlet side.
6. Apparatus according to claim 1 characterized in that temperature
sensors (32, 36) are fitted to the end sections of each pipe (14,
16) on its inlet side.
7. Apparatus according to claim 1 characterized in that a
temperature sensor (28) is connected to the temperature-controlling
member (12).
8. Apparatus according to claim 1 characterized in that the
temperature-controlling member (12) and the pipes (14, 16) have a
U-shaped construction.
9. Apparatus according to claim 8 characterized in that the
temperature sensor (28) connected to the temperature-controlling
member (12) is seated on a plate (26) connecting the two sides of
the U-shaped temperature-controlling member (12).
10. An apparatus for controlling the temperatures of a plurality of
liquid streams comprising in combination
(a) a first metallic pipe for transporting a first liquid,
(b) a second metallic pipe for transporting a second liquid,
(c) first pump means for causing said first liquid to move through
said first pipe and second pump means for causing said second
liquid to move through said second pipe, and
(d) an elongated electrical heating element for generating
heat;
said elongated electrical heating element being joined directly to
said first metallic pipe along a substantial portion of its length
in a heat conducting manner so that the heat generated by said
heating element will be imparted by conduction to said first
metallic pipe,
said second metallic pipe being joined directly to said first
metallic pipe along a substantial portion of its length in a heat
conducting manner so that a portion of the heat imparted to said
first metallic pipe by said electrical heating element will be in
turn transferred by conduction to said second metallic pipe,
the thermal impedance between said electrical heating element and
said first metallic pipe being less than the thermal impedance
between said electrical heating element and said second metallic
pipe.
11. An apparatus according to claim 10 wherein the wall thickness
of said first metallic pipe is different from that of said second
metallic pipe.
12. An apparatus according to claim 10 wherein the metal of said
first pipe is different from that of said second pipe.
13. A method for establishing a temperature difference in a
plurality of liquid streams flowing through separate metallic pipes
which comprises
(a) generating heat in the liquid in one of said metallic pipes by
positioning an electrical heating element in direct heat conducting
engagement with said one of said metallic pipes,
(b) generating heat in the liquid in another of said metallic pipes
by joining said another metallic pipe to a portion of said one of
said metallic pipes along a portion of its length,
(c) controlling the flow of liquids through said metallic pipes,
and
(d) establishing a thermal impedance between said electrical
heating element and said one of said metallic pipes that is less
than the thermal impedance between said electrical heating element
and said another of said metallic pipes.
Description
The invention relates to an apparatus for regulating the
temperature of a plurality of liquids.
Known apparatus of this type comprise a plurality of
temperature-regulating members serving for heating and/or cooling,
which are each associated with one of the liquids of which the
temperature is to be regulated. Immersed respectively in the
liquids of which the temperature is to be regulated is a
temperature sensor and a central control device receives the output
signals of the latter and controls the individual
temperature-regulating members so that a predetermined temperature
relationship between the individual liquids is maintained.
Temperature-regulating apparatus of this type indeed allow an
adjustment of the temperature differences of the various liquids
within wide ranges; however they are expensive as regards apparatus
and if one of the temperature sensors fails it is possible that the
desired temperature relationship between the various liquids is no
longer maintained. However, for various applications, for example
regulating the temperature of the developer liquid and of the
fixing liquid in an automatic developing machine, it is necessary
that at all events one liquid has a lower temperature than the
second liquid. Otherwise irreparable damage may occur to the
material being developed.
The present invention therefore intends to provide an apparatus for
regulating the temperature of a plurality of liquids, in which
independently of the correct operation of a temperature
regulating/control device, it is always ensured that certain
temperature ratios are maintained between the liquids of which the
temperatures are to be regulated.
This object is achieved according to the invention by a
temperature-regulating apparatus described hereinafter.
Since in the temperature-regulating apparatus according to the
invention only a single temperature-regulating member is provided
and the pipes for the various liquids of which the temperatures are
to be regulated are connected to the latter by way of various, the
direction of the desired temperature gradient between the liquids
is necessarily guaranteed by the guidance of the heat flow and
indeed even if the heating or cooling capacity of the
temperature-regulating member, the circulation rates of the various
liquids or the ambient conditions should vary in an uncontrollable
manner in the case of disturbances.
With the above mentioned advantages, the temperature-regulating
apparatus according to the invention is also characterised by a
construction which is very simple and compact both mechanically and
electrically.
In a pipe through which one of the liquids flows is used as the
resistance member according to one embodiment increasing the
thermal impedance to one of the pipes, then the entire
temperature-regulating device has a particularly compact and
mechanically simple construction, in which case the same material
can be chosen as the raw material for the various pipes. This is of
particular advantage as regards welding the pipes together and as
regards simple storage.
The development of the invention according to another embodiment is
an advantage with regard to the setting up of great temperature
differences in the liquids of which the temperatures are to be
regulated.
With the development of the invention according to another
embodiment it is also possible to achieve very great temperature
differences, in which case, if desired, the pipes may again be
produced from the same material.
Also the development of the invention according to another
embodiment is advantageous with regard to the setting-up of great
temperature differences between the liquids.
In a temperature-regulating apparatus according to another
embodiment, with the same mechanical construction of the unit
formed by the temperature-regulating member and pipes, different
temperature differences can be set up between the liquids of which
the temperatures are to be regulated, since by increasing the
through put through the pipe connected to the
temperature-regulating member with a lower thermal impedance, the
flow of heat to the remaining pipes is correspondingly reduced.
In a temperature-regulating apparatus according to another
embodiment, the temperature of the various liquids at the outlet
side can be measured separately directly at the
temperature-regulating device.
According to another embodiment the temperature of the liquids
flowing in can be measured in a corresponding manner. Thus a
temperature-regulating apparatus, which has both the features
described above and also has the advantage that it is constructed
completely symmetrically, so that if necessary the inlet side and
outlet side can be exchanged.
If according to another embodiment a temperature sensor connected
to the temperature-regulating member is used, then by way of its
output signal a correct acceptance of the heating or cooling
capacity by the various liquids circulating through the pipes can
be controlled. An output signal of this temperature sensor rising
or falling inadmissibly sharply can be used to achieve protection
against running dry.
The development of the invention according to another embodiment is
advantageous with regard to a simple manufacture of the
temperature-regulating apparatus based on commercially available
pipe material and commercially available temperature-regulating
members.
With the development of the invention according to another
embodiment, it is possible to bring the liquid temperatures to the
desired reference temperatures particularly quickly, in that one
carries out the control of the heating or cooling capacity in the
initial stage first of all according to the difference between the
inlet temperature and reference temperature, whereas towards the
end of the regulating process one changes over to a control
depending on the difference between the outlet temperature and the
reference temperature.
The invention is described in detail hereafter by means of several
embodiments referring to the drawings, in which:
FIG. 1 is a plan view of a temperature-regulating unit for heating
two liquids to different temperatures;
FIG. 2 is a section through the temperature-regulating unit
according to FIG. 1 along section line II--II;
FIG. 3 is a block diagram of a temperature-regulating apparatus,
which comprises a temperature-regulating unit according to FIG. 1
and additional pieces of equipment for setting-up the temperature
difference between the two liquids;
FIGS. 4 to 6 are cross sectional views showing alternative
arrangements for joining an electric heating element to two
separate pipes for conducting different liquids; and; and
FIG. 7 is a diagrammatic plan view showing another possible
arrangement for two liquid conducting pipes and an electric heating
element.
In FIG. 1, a temperature-regulating unit is designated generally by
the reference numeral 10. It consists of an electrically operated
heating element 12 located at the bottom of a first pipe 14 welded
to this element and of an upper pipe 16 welded to the latter.
Seen in plan view, the heating element 12 and the pipes 14 and 16
each have a U-shaped construction and in their main section lie one
above the other in alignment. Whereas the pipe 14 is exactly
U-shaped, the pipe 16 has an end section 18 on the inlet side which
is bent outwards and an end section 20 on the outlet side which is
bent outwards. The heating element 12 similarly has bent ends
sections 22, 24.
The sides of the heating element 12 are connected approximately in
the centre of its longitudinal extent by a welded plate 26, on
which a temperature sensor 28 is seated. Temperature sensors 32, 34
are seated in a similar manner by way of clamped supports 30 on the
end sections 18 and 20 of the pipe 16 guided separately.
Corresponding temperature sensors 36, 38 are fitted to the free
ends of the pipe 14.
The pipes 14 and 16 and the outer casing of the heating element 12
as well as the plates 26 are preferably made from the same
material, for example high-grade steel, so that they can be
connected satisfactorily by welding, as indicated diagrammatically
at 40 to 50 in FIG. 2.
The above described temperature-regulating unit 10 operates in the
following manner:
The heating element 12 is heated by way of a power source not shown
in detail. Heat is transferred to the pipe 14 by thermal
conduction, so that a liquid circulated through the pipe 14 is
heated in a corresponding manner. A liquid circulated at the same
time through the pipe 16 is positively unable to reach a higher
temperature than that of the liquid circulated through the pipe 14,
since the entire supply of heat to the pipe 16 takes place by way
of the pipe 14.
If as a result of a breakdown of the circulating pump associated
with the pipe 14 and/or the pipe 16, the heat produced by the
heating element 12 is not dissipated in an orderly manner, then the
temperature sensor 28 is exposed to an increased temperature and
its output signal can be used for automatically switching off the
heating element 12.
In the temperature-regulating unit illustrated in FIGS. 1 and 2,
the temperature difference between the liquid circulating through
the pipe 14 and the liquid circulating through the pipe 16 depends
on the thermal conductivity of the materials from which the pipes
14 and 16 are made, on the wall thickness of the pipes 14 and 16,
on the thermal conductivity of the welds 44 and 46 and on the speed
of flow in the pipe 14 and on the respective heating capacity.
Whereas most of the above mentioned parameters can no longer be
influenced after the mechanical manufacture of the
temperature-regulating unit, the temperature difference between the
two liquids can still be adjusted by way of the speed of flow in
the pipe 14. It is obvious that with a very low speed of flow in
the pipe 14, the liquid circulated through the pipe 16 may reach a
temperature which is close to that in the pipe 14. If the speed of
flow in the pipe 14 is increased, then on the other hand a greater
proportion of the quantity of heat is carried away by the first
liquid.
FIG. 3 shows a temperature-regulating device with adjustable
temperature difference between the two liquids, in which case only
the pipes 14 and 16 of the temperature-regulating unit illustrated
in FIGS. 1 and 2 are shown diagrammatically. An arrow 52 symbolises
the flow of heat emitted by the heating element 12, whereas a
further arrow 54 represents the lesser flow of heat passing by way
of the pipe 14 to the pipe 16.
A control unit 56 receives the output signals from the temperature
sensors 32 to 38. The reference temperature values for the two
liquids circulating through the pipes 14 and 16 can be pre-set in
the control unit 56 by way of a keyboard 58.
The outputs of the control unit 56 are connected to the control
terminals of a first circulating pump 60 with a variable delivery
and of a second circulating pump 62 with a constant delivery. The
circulating pumps 60 and 62 draw liquid of which the temperature is
to be regulated from the tanks 64 and 66 and convey the
corresponding liquids 68, 70 through the pipe 14, 16, from which
the liquids are returned to the associated tank. The corresponding
connecting pipes, which are shown in FIG. 3 by dashes, may in
practice be formed by flexible hoses, which are simply attached to
the ends of the pipes 14 and 16 by means of hose clips.
Roughly speaking the above described control unit operates so that
it regulates the heating capacity first of all according to the
difference between the reference temperature and the temperature
measured by the sensor 36 at the inlet of the pipe 14. On
approaching the reference temperature, one then changes over to
regulation depending on the output signal of the temperature sensor
38 at the outlet side.
The output signals of the temperature sensors 32 and 34 are used to
control the delivery of the circulating pump 60, in which case
again in a first stage the control takes place according to the
difference between the reference temperature and the output signal
of the temperature sensor 32 at the inlet side, whereas on
approaching the reference temperature, regulation takes place using
the output signal of the temperature sensor 34.
From the above description of the temperature-regulating unit 10 it
is clear that the liquid circulated through the pipe 16 can
therefore never have a higher temperature than the liquid
circulated through the pipe 14, because the thermal inpedance
between the pipe 16 and heating element 12 is greater than the
thermal impedance between the pipe 14 and the heating element
12.
Whereas in the embodiment according to FIGS. 1 and 2, this
relationship between the thermal impedances is maintained on the
basis of the stacking arrangement of heating element 12 and pipes
14 and 16 chosen in this case, in the embodiment according to FIG.
4, which represents a cross section through one side of a modified
temperature-regulating unit, different materials are used for the
pipes 14A and 16A. Thus for example the pipe 14A illustrated may be
made from copper, whereas the pipe 16A is made from high-grade
steel. Both pipes are connected by welds to the heating element 12A
located therebetween. The heating element as the hottest part of
the temperature-regulating unit is thus protected against direct
contact, whereas at the same time it is again ensured that the
liquid circulating through the pipe 14 has a higher temperature
than the liquid circulating through the pipe 16.
FIG. 5 shows a similar cross section to FIG. 4, but the requirement
is made of this temperature-regulating unit that the same material
is used for the pipes 14 and 16. In the temperature-regulating unit
according to FIG. 5, the heating element 12B is also located
between the pipes 14B and 16B. In the embodiment according to FIG.
5, a higher total heat resistance between the pipes 16B and the
heating element 12B is ensured due to the fact that a tubular
resistance member 72 is introduced between the heating element 12B
and the pipe 16, but through which liquid does not flow.
In the embodiment according to FIG. 6, the heating element 12C is
welded to the contact point of two pipes 14C and 16C lying one
beside the other, in which case the pipes 14C and 16C are made from
the same material and have the same outer diameter but a different
wall thickness. In this way it is also ensured that a greater
proportion of the flow of heat emitted by the heating element 12C
passes to the pipe 14C and the liquid circulating through the
latter reaches a higher temperature than the liquid circulating
through the pipe 16C.
It was common to the above-described embodiments that in the
conveying direction of the liquid they overlapped each other to the
same extent with the heating element 12C. The different thermal
impedance resulted from the different transverse geometry of the
material.
The embodiment according to FIG. 7 shows a different total heat
resistance between the pipe 14 and heating element 12D or pipe 16D
and heating element 12D, which is also achieved with symmetrical
radial geometry of the material, since those sections over which
the pipes are in heating-conducting contact with the heating
element 12D are of different lengths. The pipe 14D follows the
heating element 12D over a greater distance than the pipe 16D, so
that the liquid circulating through the pipe 14D necessarily has a
higher temperature than the liquid circulating through the pipe
16D.
It will be understood that the "longitudinal variation" of the
thermal impedance according to FIG. 7 can be combined with the
"transverse variation" of the thermal impedance, as was described
above with reference to FIGS. 1 to 6.
* * * * *